Office-selecting means for telephone trunk circuits



Aug. 27, 1929.

- J. DAVIDSON, JR., ET AL 1,725,753 OFFICE SE LECTING MEANS FORTELEPHONE TRUNK CIRCUITS I Filed April 1928 2 Sheets-Sheet 1 .7616Switehboal'li outward Inward Ill ATTORNEY All-g- 1 J. DAVIDSON, JR., ETAL. 1,725,753

OFFICE SELECTING MEANS FOR TELEPHONE TRUNK CIRCUITS Filed April 4, 19282 Sheets-Sheet 2 Jascrilaer-{s Set ers LII I l Sadascrz'b w m 0 9 a 8.2? Tm [veal 0 E IIFIIE Ell Patented Aug. 27, 1929.

UNITED STATES 1,725,753 PATENT OFFICE.

JOHN DAVIDSON, JR., OF IVIONTCLAIR, NEW JERSEY, AND HENRY E. PHELPS, OFTUCKAI-IOE, NEW YORK, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPHCOMPANY, A CORPORATION OF YORK.

OFFICE-SELECTING MEANS FOR TELEPHONE TRUNK CIRCUITS.

Application filed April 4,

This invention relates to telephone systems and more particularly tolong distance telephone circuits and provides means whereby an operatorlocated at one point may be connected over a given long distance linedirectly to any one-of a plurality of oihces located at a distant point.

For certain types oii long distance service, it is desirable that longdistance lines 6X- tending between two points appear on the switchboardof certain local oiiices in addition to the switchboards of the tolloiiice located at one or both or such points. As an example, of this,take the usual case where the toll oliic-e is located in the businesssection or a city so that a local oliice serving the business section islocated in the same building with the toll ofiice, or in a buildingclose by. Since a large number or toll calls from a given distant pointwill terminate in this business section, a saving in time and cost orservice could be obtained by arranging toll lines from such distantpoint to appear on the switchboard of the local oil-ice in question,thus enabling the distant operator to establish a connection directlywith the local ofiice and in this way avoid'the time and expenseconsumed in establishing the usual. type of toll connection via tolloiiice and over a toll switching trunk to the local oilice. At the sametime, in order to serve the local otlices located some distance from thetoll ofiice, or to establish through toll connections between distantpoints, it would be necessary to have toll lines from the distant pointterminate at such toll office. For calls to such outlying local ofiices,a toll connection would be established in the usual manner over a tollswitching trunk.

In general, it would be uneconomical to have a group or toll'lines fromthe distant point to the toll office and a separate group of toll linesfrom the distant point to the local ofhce. On the other hand, if thesame group of toll lines were permanently con nected to the switchboardsof. both the local and toll ofiices, signaling difficulties would beencountered, for upon the distant operator ringing on a given toll line,signals would appear before both the local and toll operators withresultant confusion and loss of time before the particular type ofoperator desired was determined and connection to her established.Special circuits could be utilized between the toll switchboard locatedat the first point and either the toll or a local switchboard located atthe second point, the establishment of such connection at the secondpoint being automatically accomplished in accordance with signalstransmitted from the first point. This result is accomplished byterminating a given toll line extending from the first point upon a pairof contact arms of a selector switch at the second point. Certain groupsof contact points over which the switch arms pass are wired to a groupof multiple jacks on the toll switchboard, while certain. other groupsof such contact points are similarly wired to a group of multiple jackson the local switchboard, the arrangement being such that as the switcharms pass over the contact points in succession, the toll line isconnected alternately to the toll and local switchboard multiples. Thestepping magnet of the selector switch is connected to an interrupterwhich periodically completes the operating circuit for this magnet, inthis way causing the contact arms of the switch to be stepped slowlyaround, making contact with each set of contact points in turn. Thus,when the toll line is idle, it is automatically and continuouslyconnected to one answering multiple and then to the other, anddistinctive tones are sent out to the distant terminal to inform anyoperator who may take up the line there to which oflice the line isconnected at that moment. The distant operator waits until the propertone tells her that the desired office is connected to the toll line andthen rings. This stops the automatic switch ing mechanism and lights theproper line lamp signals. There is asilent interval between tones sothat the operator will not ring just as the switch is made and reach thewrong answering position. On calls to the distant point over the tollline in question, the switching mechanism is arranged to quickly connectthe toll line to the switchboard of the cities which originates thecall.

Having thus outlined the invention in general terms, the detailedcircuit operation will now be given. Referring to the drawings, Figure 1shows a detailed circuit embodying the invention, comprising one end ofa toll telephone circuit, together with switching means to connect saidline alternately to a toll and a local switchboard; Fig. 2, read ingfrom left to right, shows more or less schematically a subscriberstelephone ci1= cuit, atoll switching trunk, a toll cord circult, and thedistant end of the toll circuit,

the near end of which is shown in Fig. 1. Fig. 3 shows schematically thecircuit of Fig. 1 and, in addition, the upper part of the drawing showsa connection from the toll switchboard to a subscribers circuit througha toll cord and over a toll switching trunk, while the lower portion ofthe drawing shows a connection from the local switchboard through an Acord to a subscribers circuit. Figs. 2 and 3 taken in order showsschematically how a connection is established from a dist-ant subscriberover the toll line and through the switching mechanism to a subscriberthrough either the toll or the local switchboard at the near groundthrough interrupter 28. The operation of relay 25 slowly rotatesthe'shatt on which the contact arms of the selector switch are mounted.A pair of these switch arms are designated 36, but all arms are the sameand all are mounted rigidly on the same shaft so that for each operationof relay 25 the switch arms make contact with the next succeeding set ofcontacts on the arcs 8 to 13, inclusive, of the selector switch. 7

During the first five contact steps of the selector switch 7, the tollline 32 is connected to the group of toll board multiple jacks 34through arcs 8 and 9 of the selector switch. From steps 6 to 10,inclusive, the toll line is connected to the local switchboard multiplejacks 35 through arcs 8 and 9 of the selector switch. Similarly, fromsteps 11 to 15, the toll line is again connected to the toll board andfrom steps 16 to 20 to the local board. When the selector switch reachesthe last two steps, ground is connected to stepping magnet 25 throughare 12 of the switch, causing the magnet to be rapidly stepped around toits initial position. This avoids loss-of time while the switch ispassing over that part of its cycle which is too small to furnish aproper interval for terminating the toll line at one of the switchboardposit-ions. It will thus be seen that as the selector switch rotates, itconnects the toll line alternately to the toll and local switch boards.

During a portion of each such switchboard connection a source of tone 37is applied across the toll line through transformer 24, the secondarywinding of which is connected across the toll line through the pair ofupper inner back contacts of relay 2, while the'primary winding isconnected from ground to the source of tone through are 11 of theselector switch. Any source of tone might be used for this purpose. Thatshown utilizes a two electrode low pressure gaseous discharge tube inwhich the bulb is filled with some inert gas such as neon. Theoscillator circuit consists of battery connected through a highresistance 33 to a gaseous discharge tube 31 and ground, and in shuntwith the tube, a condenser of suitable capacity such as 5 0r 6. Anoscillating circuit of this type is described in the Proceedings of thePhysical Society of London, vol. 36,'page 269, June 15, 1924:. Thefrequency of oscillation is determined within limits by the magnitude ofthe capacity connected in shunt with the tube. 1

Referring now to are 11 of the selector switch, it will be not-ed thatcontacts 1 to 3 and 11 to 13 are wired to condenser 6, while contacts 6to 8 and 16 to 18, inclusive, are wired to condenser 5. Condenser 5 isof dilferent capacity from 6, thus furnishing two tones of differentfrequencies dependent upon the capacity connected across the tube at agiven time. Considering the wiring scheme of are 11 in conjunction withthat of arcs 8 and 9, it will be seen that during a part of eachinterval that the toll line is connected to the toll'board, one sourceof tone is transmitted over the toll line to the distant end, Whileduring a portion of each interval that the toll line is connected to thelocal board, a different source of tone is ap plied to the toll line,owing to the change in capacity connected across the tube 31 during therespective intervals.

Contact points 4 and 5, 9 and 10, 14 and 15, and 19 to 22 inclusive, ofare 11 areopen; hence, while the contact arms are on such steps, no toneis transmitted over the toll line. These silent intervals. it will beobserved, occur just prior to a disconnection of the toll line from oneswitchboard and its subsequent connection to the other, the change beingaccomplished the arms of the selector switch pass from 5 to 6, 10 to 11,15 to 16 and 20 back to 1. The silent intervals thus serve to warn thedistant operator that a change in switchboard connection is being madeso that she will not attempt to establish connection with a switchboardduring such interval; otherwise in a number of instances she would beconnected to the wrong ofiice.

Assume now that the toll operator at office F of Fig. 2 desires toestablish a connection between subscribers sets 85, Fig. 2 and 69, Fig.3, the latter being reached through the toll ofiice G. She establishesconnection with subscribers set 35 in the usual manner by connectingtoll cord 88 to toll switching trunk 86 and instructs the operator atlocal ohice E to connect the incoming end of such switching trunk tosubscribers set 85. Upon connection of toll cord 88 to switching trunk86, battery supplied through retard coil 51 at office E sends currentout over the toll switching trunk and through retard coil 52 and relay54 in the toll cord circuit 88. Relay 54 operates and lights lamp 53which. lamp remains lighted until the subscriber at answers.

Meantime the operator at oilice F connects plug 56 of the toll cord tojack 57 of the toll line. Battery supplied from the sleeve of the tollcord operates relay 59 which in turn disconnects relay 58 from acrossthe toll line. The operator at ofiice F connects her telephone set 91across the toll cord and. listens on the circuit until she hears thetone transmitted from the automatic switching device 94, Fig. 3,corresponding to the toll office connection and rings on the circuit byoperating ringing key 55. This ringing current upon arriving at theswitching device 94 flows through and operates relay 1, refer here toFig. 1. The operation of relay 1 in turn furnishes ground to operaterelay 3 over a circuit from battery through the lower outer back contactof relay 2 through the winding of relay 3 to ground at relay 1. Theoperation of relay 3 in turn connects ground to the lower winding ofrelay 4, causing it to operate. Relay 4 immediately locks up through itsupper winding on a circuit from battery 23 through the lower outer backcontact of relay 2, upper inner front contact of relay 4. through theupper winding of the latter relay to ground. The operation of relay 4opens the circuit from interrupter 28 to stepping relay 25 at the upperouter back contact of relay 4. This prevents further operation ofstepping relay 25 and maintains the toll line connected to the desiredswitchboard multiple. The operation of relay 4 also causes the busydrops 16 and 17 over the toll board multiple jacks to be operated on acircuit from battery through the lower front contact of relay 4 throughthe busy drops 16 and 17 to ground. Relay 4, upon operating, also causesthe lighting of line lamps 18 at the toll board inward positions. Thecircuit is traced from battery through the upper intermediate frontcontact of relay 4, through are 10 of the selector switch through thewinding of relay 26 to ground. The conscquent operation of relay 26connects battery through its upper front contact to light lamps 18.Referring for a moment to are 10 of the selector switch, it will benoted that relay 26 is connected to the contact points of all steps onselector switch 7 for which a connection between toll line and tollboard is established through arcs 8 and 9. Furthermore, for all stepsestablishing a connection to the local board, the contacts of are 10 arewired directly to lamps 21 over the local board answering jack. Relay26, upon operating, also connects battery 19 through its lower frontcontact, through the upper back contact of relay 27 to the sleevecircuit of the local board multiple, thus furnishing a busy test signalat the local board.

Soon after lamps 18 are lighted in the manner described above, a tolloperator at office G, Fig. 3, answers by connecting plug 62 of toll cord89 to jack 61. Jack 61 of Fig. 3 represents any one of the groups ofjacks 14 and 15 of Fig. 1. For convenience, only one such jack 61 isshown in Fig. 3. Battery supplied from the sleeve of the toll cord 89,Fig. 3, flows through the sleeve circuit of jacks 14 of Fig. 1, throughrelay 27, lower inner back contact of relay 29, to ground through arc 13of the selector switch causing relay 27 to operate. Are 13 of theselector switch is wired to furnish ground to relay 27 for all selectorswitch steps connecting the toll line to the toll board, and is similarlwired to furnish ground for relay 29 for all selector switch stepsconnecting the toll line to the local board. Relay 29 will be referredto later. 7

The operation of relay 27 connects ground through its lower outer frontcontact to the winding of relay 2 causing its operation. he operation ofrelay 2 disconnects the secondary winding of tone transformer 24 at theupper inner back contacts of relay 2, and opens the operating circuit ofrelay 1 at the upper outer back contact of relay 2. In addition theoperationof relay 2 releases relay 3, if still operated, bydisconnecting battery therefrom at the lower outer back contact of relay2. The operation of relay 2 opens the holding circuit for relay 4 bydisconnecting battery 23 from the upper winding of relay 4 causing itsrelease. The re lease of relay 4 disconnects battery from its upperintermediate front contact causing the release of relay 26, which inturn disconnects battery from lamps 18 causing their extinction. Therelease of relay 26 does not re move the busy test from the local boardsleeve circuit since upon the operation of relay 27, battery 19 isconnected directly to the local board sleeve multiple through the upperfront contact of relay 27 in anticipation of the release of relay 26.The operation of relay 2 supplies battery through its l lower outerfront contact to hold the busy drops 16 and 17 operated after relay 4 isreleased. Furthermore, relay 2, upon operating, opens at its lower innerback contact the operating circuit of relay 25, thus holding theselector switch stationary after the release of relay 4 has closed theoperating circuit of relay at the contacts of relay 4. This completesthe cycle of operations of the selector switch mechanism of Fig. 1 forthe time being and leaves the circuit ready for speech.

Referring now to Figs. 2 and 3, the toll operator at ofiice Gr afterobtaining the called number from the operator at ofiice F, establishes aconnection to subscribers set 69 in the usual manner by connecting tollcord 89 to toll switching trunk 87 and instructing the operator at localoflice C to connect the incoming end of the switching trunk to thesubscribers line. Upon the connection of toll cord 89 to trunk 87, relay65 operates as shown on battery supplied from office C through retardcoil 68 and retard coil 64 at ofiice G. Relay 65 upon operating closesthe circuit to light lamp 66, which lamp remains lighted until thesubscriber at 69 answers. The operator at oflice G upon receiving asignal that trunk 87 is connected to subscribers set 69, operatesringing key 92 to ring on the subscribers circuit 69. When thesubscriber at 69 answers, relay 70 operates and opens the operatingcircuit for relay 65 at office G which releases and extinguishes lamp66. Meantime the operator at ofiice F operates ringing key 93 to ring inthe subscriber at 85. Upon answer of the latter subscriber, relayoperates causing lamp 53 at oiiice F to be extinguished.

\Vhen the call is complete and the subscribers hang up, relays 50, Fig.2 and 70, Fig. 3 release, causing lamps 53 and 66 to relight. Theoperator at office F, upon noting the lighted lamp 53, disconnects tollcords 88 from the switching trunk and tell line. The disconnection ofthe toll cord from the switching trunk furnishes a sig nal, not shown,to the operator at office E who thereupon disconnects the switchingtrunk from the subscribers line. The disconnection of the toll cord fromthe toll line releases relay 59. In a similar way, the operator atoffice G upon noting the lighted lamp 66, disconnects toll cord 89 fromthe switching trunk, thus causing the operator at office C to disconnectthe switching trunk from subscribers line 69. The disconnection of plug62 from jack 61 starts a cycle of operations which restores the selectormechanism of Fig. 1 to its normal condition. Referring to Fig. 1, theremoval of the toll cord from jack 14 removes battery from the sleevecircuit, and thus causes the release of relay 27-. The release of relay27 disconnects battery from the sleeves of the local board jacks 20 and22 at the upper front contact of 27 and removes ground from the windingof relay 2 at the lower outer front contact of 27 causing the release ofrelay 2. The release of relay 2 connects relay 1 across the toll lineand restoresthe signal tone supplied through transformer 24 to the tollline. In addition, the release of relay 2 disconnects battery from busydrops 16 and 17, causing their release, and closes the circuit frominterrupter 28 to stepping relay 25, whereupon the latter relay resumesoperation in accordance with the current pulses supplied from theinterrupter.

Had the operator at oflice F,'Fig. 2, wished to connect the subscribersset 85 to subscribers set 84 instead of to 69, her procedure would bethe same as that outlined above with the exception that she would ringon the toll line by operating key when she heard the tone telling herthat toll line 32 of. Fig. 2 was connected to the localoifice D.Referring now to Fig. 1, in this: case the ringing current would againoperate relay 1, which in turn would cause the operation of relays 3 and4. The busy drops 16 and 17 would be operated from relay 4. The currentfor the stepping relay 25 would be opened at the contacts of relay 4When the selector switch was on a step connecting the toll line tot-helocal switchboard 35. Battery supplied from the upper intermediate frontcontact of relay 4 operates lamps 21 through are 10 of the selectorswitch. The local operator upon noting the lighted lamp, connects plug72, Fig. 3, of an A cord circuit 90 to jack 71. Jack 71 of Fig. 2represents any of the jacks 20 or 22 of Fig. 1. Battery supplied fromthe sleeve of the A cord circuit 90 furnishes a busy test for the sleevecircuit of jacks 20 and22 and sends currentthrough the A cord lamp 76,Fig. 2, through the upper back contact of relay 27, Fig. 1, lower backcontact/of relay 26 through the winding of relay 29, lower inner backcontact of relay 27 to ground through are 13 of the selector switch.Lamp 76, Fig. 2, does not light, due to the fact that it is shunted outby resistance 75 being connected across it upon the operation of relay77. An operating circuit for the latter relay is completed throughretard coil 30 of Fig. 1. Relay 29, Fig. 1, operates over the circuitdescribed above and connects ground at its lower outer front contact tooperate relay 2, the operation of which in turn releases to the sleevecircuit.

84:, and then operates ringing key 98. Upon connecting the .A cord tothe subscribers line, lamp 80 li hts from battery to ground over thesleeve circuit of the subscribers line. hen the subscriber at 84answers, relay 78 operates and extinguishes lamp 80. When the call iscompleted and the subscribers hang up, lamps 53 and 80 relight and theoperators at offices F and D disconnect their respective cord circuits.The effect of disconnecting toll cord 88 was described above.

pon disconnection of plug 72 from jack 71, Fig. 2, relay 29 of Fig. 1releases, in turn releasing relay 2. The release of relay 2 restores thecircuit of Fig. 1. to its normal condition as described above.

On a call to the distant subscribers circuit 85, Fig. 2, either the tollor the local operator at the near end of the toll line Fig. 3 can obtainaccess to said toll line by connecting a cord circuit to jacks 61 or 71,as

the case may be. Assume that the toll opcrater wishes to use the line.She connects plug 62 to jack 61, thus furnishing battery Referring toFig. 1, battery on the sleeve circuit of multiple 34 operates relay 27irrespective of the position of the stepping magnet at the moment thetoll cord is connected. If at that moment the toll line is connected tothe toll board, the operating circuit of relay 27 would be from batteryon the sleeve of multiple 34,

through the winding of relay 27, back contact of relay 29, to groundthrough are 13 of the selector switch. If at the moment of inserting thetoll cord, the toll line were connected to the local board, theoperating circuit for relay 27 is from battery on the sleeve through 27,back contact of relay 29, lower outer back contact of relay 4: to groundthrough are 18 of the selector switch. In either case relay 27 operatesand connects ground to operate relay 2. The operation of relay 2disconnects tone transformer 24 and relay 1 from the toll line, operatesthe busy drops at the toll board and opens the interrupter circuit torelay 25. The operation of relay 27 also connects battery 19 to thesleeves of jacks 20 and 22 for a busy test and opens the circuit ofrelay 29 at the lower inner back contact of relay 27 to prevent relay 29from operating should a plug be inadvertently inserted in a local boardjack while the line is held at the toll board.

If at the moment the toll cord is connected to the toll board multiplethe selector switch is 011 a step connecting the toll line to the tollboard, the cycle of operations is complete as described above. If,however, at the moment of such connection the toll line is connected tothe local board, a circuit is closed upon the operation of relay 27which operates the stepping relay 25 and causes this relay to step theselector switch rapidly around until the toll line is connected to thetoll board multiple. To see how this circuit operates, suppose that atthe moment the toll operator plugged into jack the selector switch wason step 6. In that event a circuit would be traced from battery, throughthe winding and back cont-act of relay 25, through are 12 of theselector switch, lower inner front contact of relay 27 to ground throughare 13, since the contact arm of this are is also on step 6. Thiscircuit, it will be seen, is closed until the selector switch passes onto step 11. Consequently, the stepping relay will operate and rapidlystep the selector switch around until the switch arms rest on step 11.When this occurs, the circuit will be traced from the stepping relaythrough are 12 to an open circuit at the lower inner front contact ofrelay 29, which will prevent the further operation of relay 25 and thusmaintain the toll line connected to the toll switchboard.

The toll operator at o-fiice G of Fig. 3 now rings on the line byoperating the ringing key 63. This ringing current arriving at oflice Fof Fig. 2 flows through relay 58 causing it to operate and connectbattery through its front contact to operate relay 60. Relay immediatelylocks up on a circuit from battery through the upper back contact ofrelay 59, upper front contact of relay 60, to ground through the relaywinding. The operation of relay 60 lights the line lamp 97 associatedwith the distant end of the trunk. The toll operator at office F, onnoting the lighted lamp, connect-s plug 56 to jack 57. Current suppliedfrom battery 96 thereupon flows through relay 59, causing its operation.The operation of relay 59 disconnects relay 58 from across the tollline, releases relay 60 and thus extinguishes lamp 97. From this pointon the circuit operation is the same as that described above on a callfrom subscribers set 85 to set 69.

, Had the call originated at the local ofiice D, plug 72 would beconnected to jack 71. Referring to Fig. 1, battery on the sleeve ofmultiple 35 would operate relay 29 to ground through are 13 of theselector switch if at the moment of connection the toll line wereconnected to the local board, otherwise the circuit would be tracedthrough the lower outer back contact of relay 4.- to ground at are 13.In either case relay 29 would operate and furnish ground to operaterelay 2 with the results described above for a call originating at thetoll oflice G.

The cycle of operations would thus be complete if at the moment ofconnecting the cord circuit the toll line is connected to the localboard. If not, a circuit is closed to step the selector switch rapidlyaround until this is accomplished. Assume that when the cord is insertedthe selector switch is on step 1. A

relay 29 to ground through are 13, This circuit operates 25 until theselector switch passes on to step 6, when the circuit is traced frombattery through relay 25, and arc 12, to

' an open circuit at the lower inner front contact of relay 27, thuspreventing the further operation of relay 25.

.It should be added here that in the present instance when relay 29operates it opens the operating circuit for relay 2? to prevent theoperation of this relay in case a cord-is inadvertently connected to thetoll board jacks during the holding period. The circuit operation fromthis point on has been described immediately above.

In the explanation given above, the specific case is considered whereone end only of a toll line is connected alternately to the toll boardand one local board multiple. It can easily be seen, however, that bymeans of minor circuit modificationsthe same scheme could be used forconnecting the toll line to the toll board multiple and to any desirednumber of local board multiples in order, or

to a plurality of toll board and local board multiples, or tea pluralityof switchboard mutiples in general. Furthermore, the scheme is notrestricted to one end of a toll line only but can be applied at bothends so that an operator at either end may select any one of a number ofotlices at the distant end to which she desires the toll line inquestion to be connected.

WVhat is claimed is:

1. In a telephone system in combination, a'telephone trunk circuitextending from a. first to a second point, a telephone switchboardlocated at such first point in which the telephone circuit terminates, aplurality of switchboards located at the second point,

switching means at such second point to connect automatically andperiodically the telephone circuit in progression to telephone circuitmultiples individual to each of the switchboards at such second point,means for automatically transmitting over the telephone circuit from-thesecond to the first point during a portion of each switchboardconnection at the second point a signal which is "different for eachsuch CODHGCJiOIl, means controlled from the first point for causing thedisconnection of the signal means last mentioned from the telephonecircuit and for arresting the further operation of theautomaticswitching means to hold the tele phone circuit connected to apredetermined switchboard at the second point, means upon sucharrestment for operating signaling means at the switchboard thusconnected, means controlled from the switchboard thus connected forcausing the telephone circuit multiples at the plurality of switchboardsat the second point to appear busy and to; extinguishing the signalingmeans at the switchboard connected to the telephone circuit, meanscontrolled from the switchboard thus connected to the telephone circuitat the'second point for startlng anew the progression oi": the automaticswitching means which connects the telephone circuit to the plurality ofswitchboards, and means controlled trom any switchboard at the secondpoint for causing the telephone circuit to be quickly connected to suchswitchboard and tor arresting the progression. of the autoatic switchingmeans thereafter until released at such switchboard.

2. in a telephone system in combination, a telephone trunk circuitextending from a first to a second point, a plurality of telephoneswitchboards located at the first point, a plurality of telephoneswitchboards located at the second point, means at the first point 7 toconnect automatically and periodically the trunk circuit in progressionto telephone circuit multiples individual to each of the plurality ofswitchboards such point, switching means at the second point toaccomplish a similar result at such point, means for transmitting fromthe first to the second point during a portion of each switchboardconnection atthe first point a signal different for each switchboard connection, means for similarly transmitting signals from the second to thefirst point during a portion of each switchboard connection at thesecond point, means controlled from the second point for stopping thetrans mission of signals to such point and for simultaneously arrestingthe operation of the automatic switching means at the first point tohold the telephone circuit connected there to a predeterminedswitchboard, means controlled from the first point to accomplish similarresults at the second point, means upon such arrestment oi the automaticswitching means at either point for operating signals at the switchboardthus connected to the telephone circuit during illrestment, meanscontrolled from the switchboard thus connected to cause the telephonecircuit multiples of the plurality of switchboards at such point toappear busy, said means further operating to extinguish the signal meansat the switchboard connected to the telephonecircuit, means controlled"from the switchboard thus connected to the telephone circuit forstarting anew the progression of the automatic switching means at suchpoint and for again transmitting signals to the distant point, and meanscontrolled from any switchboard at either point to cause the trunkcircuit to be quickly connected to such switchboard thereafter to arrestthe progression of the automatic switching means under control of theswitchboard thus connected.

3. In telephone system in combination, a toll telephone circuitextending from a first to a second city, a toll switchboard at the firstcity in which the toll circuit is terminated, a toll switchboard and alocal switchboard at the second city each equipped with a plurality oftrunk multiple calling and answering jacks, switching means at suchsecond city to connect automatically and periodically the toll circuitalternately to said local and toll switchboard multiple jacks, means fortransmitting from the second to the first city during a portion of eachswitchboard connection at such city a characteristic tone different foreach switchboard connection, means at the second city controlled byringing current transmitted from the first city for disconnecting thesignal tones from the toll circuit and for arresting the operation ofthe automatic switching means at such second city to hold the toll lineconnected to a predetermined oflice at such city in accordance with theswitchboard connectlon established at the moment when the ringingcurrent is applied, means at the second city upon such arrestment i'oroperating busy drops associated with said trunk multiple jack on saidtoll switchboard, means upon such arrestment for lighting line lamps atsaid answering jacks on the switchboard connected to the toll line,means for extinguishing such line lamps and for connecting a busy testto the sleeve circuits of said multiple jacks at, both the local andtoll switchboards upon connection of a link circuit to one suchanswering jack, means for starting anew the operation of the automaticswitching means and for reapplying the signal tones to the toll lineupon disconnection ot the link circuit from the answering jack, andmeans at the second city for quickly connecting the toll circuit to themultiple of a switchboard which originates a call and for arresting theoperation of the automatic switching means in that position uponconnection of a link circuit to such switchboard multiple and forrenewing again the progression of the switching means upon disconnectionof such link circuit.

i. In a telephone system in combination, a toll telephone circuitextending from a first to a second city, a toll ofiice at the first cityin which the toll circuit is terminated, a toll oifice and a pluralityof multiple offices located in the second city, switching means at thesecond city to connect automatically and periodically the toll circuitin progression to the toll office and the plurality 01 local offices,means for automatically transmitting from the second to the first cityduring a portion of each period that the toll circuit is connected to anoffice at such city a characteristic tone different for each officeconnection, means at the second city controlled by ringing currenttransmitted from the first city for disconnecting the signal tones fromthe toll circuit and for arresting the operation ot the automaticswitching means at the second city to hold the toll circuit connected toa predetermined oiiice in accordance with the moment at which theringing current is applied, means upon such arrestment to operate busydrops associated with the toll line multiple jacks atthe toll board,means upon such arrestment for oper ating signals at the answeringpositions of the ofiice to which the toll line is thus connected, meansfor extinguishing the signals at the answering positions and forconnecting a busy test to the sleeve circuits of the toll line multiplejacks at the plurality of offices upon connection of a link circuit toone such toll line answering jack, means for again connecting the signaltones to the toll circuit and for starting anew the progression of theautomatic switching means upon removal of such link circuit from the answering jack, and means at the second city for quickly connecting thetoll circuit to any of the plurality of oifices at the second city uponconnection of a link circuit to the toll circuit multiple at such ofiiceand for suspending the further operation of the automatic switchingmeans during the period that the link circuit is thus connected at suchoifice.

5. In a telephone system in combination, a trunk circuit extending froma first to a second point, a telephone switchboard lo cated' at thefirst point in which said trunk circuit terminates, a plurality ofswitchboards located. at the second point, switching means at the secondpoint to connect automatically and periodically the telephone circuit inprogression to each of the switchboards at the second point, means forautomatically transmitting over the telephone circuit from the second tothe first point during a portion of each switchboard con nection at thesecond point a signal which is diiierent for each switchboardconnection,

means controlled from the first point for causing the disconnection ofthe signal means last mentioned and for arresting the further operationof the automatic switching means to hold the telephone circuit connectedto a predetermined switchboard at the second point, means controlledfrom the switchboard thus connected to the trunk circuit at the secondpoint for releasing said trunk circuit and for starting anew theprogression of the automatic switching means, and means controlled fromany switchboard at the second point for causing the telephone circuit tobe quickly connected to such switchboard and for arresting theprogression of the automatic switching means thereafter until releasedat such switchboard.

6. In a telephone system in combination, a telephone trunk circuitextending from a first to a second point, a switchboard at the firstpoint in which said trunk circuit terminates, a plurality ofswitchboards at the second point, switching means at the second point toconnect automatically and periodically the telephone circuit inprogression to each of the switchboards at the second point', a variablesource of tone at the second point comprising in series connection asource of direct current voltage, a resistance of predeterminedmagnitude and a two-element low pressure. gaseous discharge tube, a.plurality of condensers each of a different predetermined capacity tofurnish a different tone when connected in shunt with said dischargetube, a tone output circuit connected to said telephone trunk circuitand switching means for automatically connecting in shunt with saidgaseous discharge tube during a portion of each switchboard connection aseries circuit consisting of a condenser different for each switchboardand said tone output circuit, means for arresting the progression of theautomatic switching device to hold the trunk circuit connected to apredetermined switchboard at the second point upon reception of a signaltransmitted from the. first point, means controlled from saidswitchboard thus connected at the second point for releasing said trunkcircuit and starting anew the progression of the automatic switchingmeans, means controlled from any switchboard at the second point forquickly connecting the trunk circuit to such switchboard and forarresting the further progression of the automatic switching means untilreleased at such switchboard.

7. In a telephone system the combination with a circuit forautomatically connecting a telephone circuit in progression toaplurality of switchboards substantially as described in thespecifications of a variable tone source comprising in series connectiona source of direct current potential, a resistance of predeterminedmagnitude and a two-element low pressure gaseous discharge tube, aplurality of condensers each of a different predetermined capacity toproduce a desired tone, a tone output circuit connected to saidtelephone circuit, and automatic switching means adapted during aportion of each switchboard connection to connect in shunt with thegaseous discharge tube a series circuit consisting of a condenserdifferent for each switchboard and the tone output circuit.

8. In a telephone system, in combination, a line extending from a firstto a second point, a plurality of circuits at the second point,switching means thereat to connect automatically and continuously saidline in progression to said plurality of circuits for predeterminedintervals, means for automatically transmitting over said line to thefirst point during a portion of each such connection a distinctivesignal, different for each said circuit connection, means responsive tosignals from the first point for disconnecting said distinctive tone andfor arrestingthe progression of said switching means at a desiredcircuit connection, and means controlled from said circuit thusconnected for starting anew the automatic progression of said switchingmeans- 9. In a telephone system, in combination, a line extending from afirst to a second point, a plurality of circuits at the second point,switching means thereat to connect automatically and continuously saidline in progression to said plurality of circuits for predeterminedintervals, means for auto matically transmitting over said line to thefirst point during a portion of each such connection a distinctivesignal, different for each said circuit connection, means responsive tosignals from the first point for disconnecting said distinctive tone andfor arresting the progression of said switching means at a desiredcircuit connection, means controlled from said circuit thus connectedfor starting anew the automatic progression of said switching means, andmeans controlled from any said circuit at the second point for causingsaid line to be quickly c0nnected thereto and for arresting the furtherprogression of said switching means.

In testimony whereof, we have signed our names to this specificationthis 3rd day of April, 1928, I

JOHN DAVIDSON, JR. HENRY E. PHELPS.

